Field of the Invention
This invention relates to water-in-oil explosive compositions and, more specifically, to cap sensitive emulsion explosives. In another aspect, this invention relates to emulsion explosive compositions which are capable of achieving favorable incendivity and 1/2 cartridge gap sensitivity properties, while exhibiting excellent stability.
Description of the Prior Art
Water-in-oil emulsion type blasting agents were first disclosed by Bluhm in U.S. Pat. No. 3,447,978. These emulsion type blasting agents were very coarse, of low sensitivity and reduced shelf life. The agents contained an aqueous solution of inorganic oxidizer salts that was emulsified as the dispersed phase within a continuous carbonaceous fuel phase, and a uniformly distributed gaseous component. Later, cap sensitive emulsion explosive compositions were produced using explosive additives such as trinitrotoluene (TNT), and pentaerythritol tetranitrate (PETN). See, e.g., U.S. Pat. No. 3,770,522. Water-in-oil emulsion explosive compositions have also been made cap sensitive by the addition of nonexplosive detonation catalysts. In this regard, see, e.g., U.S. Pat. Nos. 3,715,247 and 3,765,964. Most recently, cap sensitive water-in-oil emulsion type explosive compositions, containing neither explosive ingredients nor detonation catalysts, have been disclosed in U.S. Pat. Nos. 4,110,134, 4,149,916 and 4,149,917.
Other water-in-oil emulsion type blasting agents are disclosed in U.S. Pat. Nos. 3,674,578, 4,470,855 and 4,216,040. The first, U.S. Pat. No. 3,674,578, issued to Cattermole et al, discloses an emulsion type blasting agent containing an inorganic oxidizing salt, a nitrogen-base salt, water, water-insoluble organic fuel that forms a continuous oil phase, a lipophilic emulsifier and gas bubbles. It is alleged that the combination of nitrogen-base salt and gas bubbles in the water-in-oil emulsion results in a blasting agent that is safe yet sensitive to detonation. U.S. Pat. No. 4,470,855, issued to Bampfield, discloses a water-in-wax emulsion explosive composition wherein the continuous carbonaceous fuel phase comprises paraffin wax together with a minor amount of a rheology modifier and stabilizer combination comprising an ethylene-containing polymer and a low molecular weight hydrocarbon liquid. U.S. Pat. No. 4,216,040, issued to Sudweeks et al, discloses an emulsion blasting composition having a discontinuous aqueous phase, a continuous oil or water-immiscible liquid organic phase, and an emulsifier having an unsaturated hydrocarbon chain for its lipophilic portion.
While the cap sensitive emulsion explosive compositions disclosed in the above-identified patents satisfy a wide range of requirements, there are certain blasting applications in which even higher sensitivities than are available using such compositions would be advantageous. For example, in coal mining where it is especially important that a string of cartridges be able to propagate the explosion from one cartridge to the next. One-half cartridge gap sensitivity tests are used to determine the suitability of the explosive for use in such applications. Basically, this test measures sensitivity in terms of the length of the air gap across which one half of a standard cartridge (11/4" by 8" in length) of explosive material can detonate a second half of a cartridge. Thus, for example, the preferred cap sensitive emulsion explosive compositions as prepared according to the disclosures of U.S. Pat. No. 4,110,134, have an air gap sensitivity of about two inches. As noted above, however, cap sensitive compositions having sensitivities greater than those generally available in cap sensitive emulsion explosive compositions are desirable in certain blasting applications, e.g., a gap sensitivity of at least about three inches.
Various formulations have been attempted in order to achieve improved sensitivity. For example, U.S. Pat. No. 4,547,232 discloses a high density emulsion blasting agent of improved sensitivity by utilizing an effective amount of a special sensitizing formulation in total or partial substitution for gas entraining density control agents. The sensitizing formulation was comprised of a polynitrate ester of a 2-5 carbon polyhydric alcohol, nitrocellulose and ammonium nitrate. Note also U.S. Pat. No. 4,383,873, issued to Wade and Fillman, which discloses cap sensitive emulsion explosive compositions comprising a discontinuous aqueous oxidizer salt phase, a continuous carbonaceous fuel phase, and closed cell void containing materials, which compositions exhibit increased sensitivity due to a reduced water content in the range of from about 4% to less than about 10% by weight of the emulsion matrix used to prepare the composition. U.S. Pat. No. 4,371,408, issued to Fillman, also discloses a sensitive, low water containing water-in-oil emulsion explosive composition wherein increased gap sensitivity is achieved by employing an emulsion matrix of reduced water content, i.e., less than about 10%, in combination with an amine sensitizing agent and a relatively minor portion of a detonation catalyst, such as copper chloride.
Though the foregoing compositions have achieved some success in the formulation of a sensitive blasting agent, there is, however, only one permissible emulsion high explosive in the U.S. market today. While other cap sensitive emulsion explosives may be made, problems in their method of preparation and achieving an air gap sensitivity of at least 3 inches, which is an important requirement of the Bureau of Mines, have prevented such emulsion explosives from achieving certification by the Bureau of Mines.
The sensitizer used in the foregoing permissible emulsion explosive is ethylene diamine dinitrate (EDDN) in an amount of 4 percent to about 6 percent. In its preparation, the EDDN is dissolved in the oxidizer solution of one or more inorganic salts at 210.degree. F. to 220.degree. F. The sensitizer solution is then subjected to tremendous mechanical agitation with fuel. The mechanical agitation breaks the solution into tiny droplets of from 2 to 6 microns which become covered with fuel, thereby forming an emulsion. The EDDN sensitized oxidizer solution, however, is not regarded as safe.
Thus, problems in the safety, simplicity and economy of the composition, as well as the stability of the agents also arise and are important considerations. This is particularly true for the low water emulsion compositions, e.g., from 4 to 10% by weight water of the emulsion matrix, as they exhibit a tendency to become dry upon aging. The compositions become dry, crumbly and hard upon aging, thus making the product less sensitive. It would therefore be of great value to the industry if an economical, stable and sensitive explosive composition were available, i.e., a composition having a gap sensitivity of at least about three inches, without a sacrifice in the stability of the composition.
As well, most water-in-oil emulsion explosives exhibit a poor ability to withstand an underwater shock wave, often resulting in total failure of an explosive in the near vicinity of a first detonated cartridge. The common type of water-in-oil emulsion explosive with no extra chemical sensitizer sometimes fails to shoot even at a distance of 21/2 feet from the first cartridge. An emulsion explosive exhibiting an improved ability to withstand underwater wave compression (dead pressness) would be of great value to the industry.
Accordingly, it is an object of the present invention to provide a novel water-in-oil explosive emulsion composition which has a gap sensitivity of at least about three inches.
Another object of the present invention is to provide such a composition which is also economical and exhibits good stability.
Still another object of the present invention is to provide such a novel water-in-oil explosive emulsion composition which comprises at least 10% by weight water, and has a density of at least about 1.0 g/cc.
Another object of the present invention is to provide a novel water-in-oil explosive emulsion composition which exhibits an improved underwater shock compression distance.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description and the appended claims.